Zebra mussels, and other invasive species such as quagga mussels, have rapidly become an expensive problem. Zebra mussels originated from the lakes of Russia and the Ukraine, and have since spread throughout the world. First noted in the Great Lakes in the 1980s, zebra mussels have quickly spread throughout many of the major lakes of the United States. Some estimate the annual cost of dealing with zebra mussels and repairing their damage to be in the hundreds of millions of dollars in the United States alone.
Removing zebra mussels from an entire lake can be problematic. The impact of a poison on the ecosystem of an entire lake, as well as the effect of introducing a large mass of dead zebra mussels, is very difficult to predict. Also, the process of getting regulatory approval for large-scale treatment has been slow. In the meantime, boat owners are left to wage their own battle against biofouling from zebra mussels, quagga mussels, and other invasive species.
It is hard to overstate the negative impact zebra mussels have on the ecology, infrastructure, and property in infested bodies of water. Zebra mussels reproduce quickly; adult females can each produce up to a million eggs a year. The free-swimming microscopic larvae, called veligers, drift in the water before settling onto any hard surface available. With respect to boats, the biofouling is not limited to the exterior surfaces of the hull, engine, and other submerged elements. Veligers that are drawn into, or swim into, engine passages can settle in the cooling system where they can grow into adults, blocking internal screens, hoses, passages, strainers, etc. Such blockages can cause an engine to quickly overheat, and extraction and repair can be very expensive.
Performance advantages and lower cost have led to the popularity of sterndrive boats, also called I/O or inboard/outboard drive boats. The hallmark feature of a sterndrive boat is that the engine is onboard, and the rest of the propulsion system is outside of the boat, passing through the transom, with the flexible connection typically protected by a baffle or bellow device. Although most outdrives can be raised up, sometimes they are still partially in the water; furthermore, an outdrive in the raised position exposes the baffle to weather and UV damage, as well as damage from animals, birds or invasive insects and sharp objects. As such, outdrives are often left in the water when the boat is moored. In zebra mussel infested waters, such exposure can lead to degraded performance and even an inoperative cooling system. While the best way to avoid mussel problems is to remove the boat from the water and rinse it with hot water, this is not always a practical solution.
Traditional methods of preventing zebra mussel growth on drives in the water have relied on using special materials, or coating surfaces with waxy or soapy substances that prevent the veligers from bonding with the surface. However, these methods are problematic, as materials can degrade over time and can be difficult to replace; furthermore, an entire coolant system would have to be rebuilt with these materials in a traditional engine. The use of coatings can be effective, but it can be difficult to determine whether an application was sufficient before mussels have started growing. Also, the use of such substances is not feasible on the internal passages of an engine, such as the cooling system.